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| Transmission won't shift from first, can shift it manually [message #335274] |
Mon, 16 July 2018 19:37  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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So we have started out on a 2 week vacation and the transmission will sometimes not shift from first gear. However I can shift it manually by pulling from Drive to second. Shifting back to Drive it will shift to 3rd.
Checked modulator and tubing and that's Ok. Checked the valve the modulator works against and it moves freely. Although I thought I might have felt a slight interference.
Installed a spare governor, but the existing one seems fine.
Seems to be fine when cold, but acts up when it gets up to operating temperature.
Hopefully it will work fine tomorrow, otherwise we will need to decide wether or not to continue.
Will I do any damage to the transmission shifting manually?
Thanks
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Transmission won't shift from first, can shift it manually [message #335280 is a reply to message #335274] |
Mon, 16 July 2018 22:23  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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This sounds like vacuum loss to the modulator to me. Several things could cause it like a cracked / leaking vacuum hose or the steel line that run along top right side of the intake manifold being plugged or partially plugged.
My non-conventional way to diagnose this would be to install a TEE in the vacuum line at the modulator and run a hose from there up and into the passenger side cockpit window. Then install a vacuum gauge and you can see if you are missing vacuum when the failure occurs.
If you already have a vacuum gauge then move it to the newly installed TEE. If it is not a vacuum to the modulator problem then we need to start looking at the governor or modulator itself
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Transmission won't shift from first, can shift it manually [message #335283 is a reply to message #335282] |
Mon, 16 July 2018 23:06 |
Brian Rust
Messages: 2
Registered: July 2018
Karma: 0
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Hi Bruce, was the governor that you took out scored at all or was it smooth? I have seen the case bores get scored and cause this problem. The bore in the case should not have any grooving and be very smooth. I don't believe it will hurt to shift it manually.
________________________________
From: Gmclist on behalf of Bruce Hislop
Sent: Monday, July 16, 2018 10:34 PM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Transmission won't shift from first, can shift it manually
Hi Ken,
I checked the modulator by first pulling the hose from the modulator and looked for transmission fluid, it was clean.
Then I put my manual vacuum pump at the manifold connection and wasn't able to hold a vacuum so the tubing is clear. Then I plugged the hose back on
the modulator and pulled a vacuum again. So this showed the tube was clear and the modulator holds vacuum.
--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
[http://www.gmcmhphotos.com/photos/data/20/IMGP2540-small.jpg]
Murray's looking spiffy
www.gmcmhphotos.com
New wheel flares, Ramco mirrors and square headlights!
My Staff says I never listen to them, or something like that
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| Re: [GMCnet] Transmission won't shift from first, can shift it manually [message #335284 is a reply to message #335282] |
Mon, 16 July 2018 23:10 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Bruce, the steel line, if it is still factory, has a crimped section at the
top, behind the engine block, and it sometimes becomes partially plugged
and restricted. Sometimes it is a problem for the modulator. I would check
that first.
Jim Hupy
Salem, Or
On Mon, Jul 16, 2018, 8:35 PM Bruce Hislop wrote:
> Hi Ken,
>
> I checked the modulator by first pulling the hose from the modulator and
> looked for transmission fluid, it was clean.
>
> Then I put my manual vacuum pump at the manifold connection and wasn't
> able to hold a vacuum so the tubing is clear. Then I plugged the hose back
> on
> the modulator and pulled a vacuum again. So this showed the tube was clear
> and the modulator holds vacuum.
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: Transmission won't shift from first, can shift it manually [message #335289 is a reply to message #335274] |
Tue, 17 July 2018 06:35 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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Brian, the bore on the existing governor is very smooth and so was the spare I installed. Valve spool Inside both seems to move freely.
Jim, I tested the metal tubing by pulling a vacuum on it from the top with the modulator disconnected. It pulled air freely through the tube, so I assume the tubing and the restriction is clear. I then plugged the modulator and pulled vacuum again using the hand pump. I held vacuum, so I assumed the tubing and modulator is good.
Ken, my Tach-Vac is Tee'd into the same hose as goes to the modulator, except at the top. It reads a range of vacuum while accelerating of about 5-12". I can't say exactly as I am usually I traffic which requires my attention. I'm not sure if I have fittings and hoses to move the tach vacuum connection down to the modulator.
Maybe the additional hose going to be Tach-Vac is upsetting the modulator operation? Y could plug that, but it's been connected like the for years.
We are about 350 miles from home, but it's freeway the whole way. Except for one gas stop, there is only two stop signs and one traffic light between here and home.
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Transmission won't shift from first, can shift it manually [message #335338 is a reply to message #335274] |
Wed, 18 July 2018 02:09 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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That is a real problem. Without it failing, it is very difficult to guess what the culprit is. I, like Jim Hupy, am still thinking a restriction at the crimp in the steel line is a good possibility. When mine became restricted years ago it failed similar to yours. I ended up removing the line and tried to blow it out. That did not work. So I attached shop air pressure to the bottom end of the steel line (out of the coach) and started heating the other end with an acetylene torch. When the end got red from heat it all of a sudden opened up from the air pressure applied to the opposite end. I painted the line gray and reinstalled it again with the factory installed crimp intact.
Before I did all of this I did have some air or vacuum flow but it was not enough to keep the modulator happy. After I cleaned it the modulator never failed to shift properly again. I am just guessing here.
Because this is intermittent, you might go get 6 feet or so of vacuum line. Run it direct from the carb port all the way to the modulator. This would eliminate the steel line and all of the existing vacuum hose. Now go run the coach normally on your next trip(s). If it doesn't fail again, I'm right. If it does fail again I guessed wrong and you are out the cost of 6 feet of hose.
Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Transmission won't shift from first, can shift it manually [message #335340 is a reply to message #335274] |
Wed, 18 July 2018 07:39 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Easy stuff and cheap stuff first. Replace vac hose top and bottom with the heavier wall type. Oil had softened the lower line enough it looked good but was bad and sucking flat. Also if you have pulled modulator you will be at "stick scribe off level" but below "running in park level" so you will need to top off ir it will be low, but you knew that.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Transmission won't shift from first, can shift it manually [message #335341 is a reply to message #335340] |
Wed, 18 July 2018 08:34 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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I learned in my younger time that it is worth pending few dollars on a new
hose and toppig of fluids.
John is very correct. When we have a coach in for handling issues, our guys
know we start with air pressure. Took over a year to convince them that we
need to start from the very basic.
On Wed, Jul 18, 2018 at 5:39 AM, John R. Lebetski
wrote:
> Easy stuff and cheap stuff first. Replace vac hose top and bottom with
> the heavier wall type. Oil had softened the lower line enough it looked good
> but was bad and sucking flat. Also if you have pulled modulator you will
> be at "stick scribe off level" but below "running in park level" so you will
> need to top off ir it will be low, but you knew that.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
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--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: Transmission won't shift from first, can shift it manually [message #335344 is a reply to message #335274] |
Wed, 18 July 2018 09:05 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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Ken,
I checked my steel line with a hand vacuum pump at the top, and the modulator disconnected. By the movement of the pump gauge I could tell there was a slight restriction but not much. Just pumping the pump itself( nothing connected), the gauge need barely moves with each pump. Connected to the tube the gauge will jump to 7" or so with each pump, then immediately drop to zero.
JohnL,
I've always found it near impossible to read a transmission fluid dipstick on any vehicle I've owned. The dipstick comes out with fluid from the side of the tube. There is no contrast between the fluid and the stick. I've drilled a couple of tiny holes at the ADD and FULL marks and that helps.
We had stopped at Al Hamilton's place, so I pulled the modulator and made sure the valve it works against was free. The coach was parked on a downhill slope and I pumped up the passenger side airbag so the modulator was on the high side of the pan. After running the engine for about a minute to pump up the convertor, I still had fluid come out when I removed the modulator, that would indicate the level was too high. I had measured the fluid level multiple times and thought it was just below the FULL mark. So I lost about 1 cup of fluid during my testing and though, well maybe I have too much, so I didn't add anymore.
Then while testing it I felt a shutter a couple of times, so we pulled into a level parking lot and pulled the dipstick a dozen times or so. Paula and I came to the conclusion it was low, so I added back the amount we lost. Then it "appeared" to be just below the full mark. The engine did stumble a couple times in the next 15 miles of driving. But I did have my computer connected to my EBL system and that showed I was losing electrical power (either battery or ignition) to the EFI system. We turned around at that point to go home and stopped at Al's again. It ran fine the 20 miles back to Al's house. I could not find any electrical issue. We continued home with no more electrical or transmission issue.
Can you elaborate on your statement " Also if you have pulled modulator you will be at "stick scribe off level" but below "running in park level". My understanding was with a hot transmission in Park, engine OFF, pull the modulator and the fluid should be at the level of the modulator. Let any excess drain, or fill it till it comes out the modulator and mark that as FULL. I had done this when I drilled the holes in the dip stick. The fluid seemed to be coming from above or around the valve as I moved it. I don't think I'm understanding this measurement. I've kept the fluid at the levels I've marked on my dipstick since 2010 when I installed a rebuilt transmission a the same time Dick Paterson rebuilt my engine.
Thanks
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Transmission won't shift from first, can shift it manually [message #335426 is a reply to message #335274] |
Fri, 20 July 2018 12:39 |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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So, I believe I have found my transmission shifting issue. I had checked the vacuum hose to be sure it had no blockage it was holding vacuum with the modulator attached.
Today I checked it again, but this time I went under while my wife pumped up the manual vacuum pump on it and watched the gauge. Suddenly it quickly lost vacuum when I touched the metal tube at the hose connection. I had Paula pump the vacuum up again and sure enough moving the hose connection cause it to lose vacuum. The hose is a 4" (or less) piece of 1/4" 30R7 fuse hose. The tube is 0.19" OD and the sealing bump on the tube and the modulator connection is 0.3" The hose looks great on the outside, no cracks anywhere. However the tube's sealing bump is very narrow. I expect it has relaxed around this bump in the tube and when it gets hot (exhaust is not far away) it softens and leaks.
Anyway, off to get a new hose and some tiny clamps!
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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| Re: Transmission won't shift from first, can shift it manually [message #335432 is a reply to message #335274] |
Sat, 21 July 2018 09:21 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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On the stick cal it's simpler than people make it. With modulator out the fluid will waterfall out the hole. Doesn''t matter hot (difficult) or cold all you are looking for is that liquid level even with bottom of hole to scribe stick as full. Then when you reassemble, you run it in park and add fluid to that new mark. The level will drop running as pump is opperating and require you to add. That is my understanding. Looks like I was on right track with lower vac hose, same place mine was bad.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Transmission won't shift from first, can shift it manually [message #335441 is a reply to message #335274] |
Sun, 22 July 2018 07:51 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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I forced the smaller hose - new piece - on the modulator and the pipe. It didn't split so I skipped the clamps. Works fine so far.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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